 <!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>不规则投影</title>
</head>
<style>	
.shadow {
	width: 200px;
	height: 200px;
	background: yellow;
	position: relative;
	filter: drop-shadow(2px 2px 10px rgba(0,0,0,.5));
}
.shadow::before {
	content: '';
	position: absolute;
	top: 50%;
	left: 100%;
	width: 0;
	height: 0;
	border: 8px solid;
	transform: translateY(-4px);
	border-color: transparent transparent transparent yellow;
}
</style>
<body>
	<div class="shadow"></div>

</body>
</html>